RE: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for merging contiguous read

[Jaegeuk Kim <jaegeuk.kim@samsung.com>]

Hi,

2013-11-18 (월), 09:37 +0800, Chao Yu:
> Hi Kim,
> 
> > -----Original Message-----
> > From: Jaegeuk Kim [mailto:jaegeuk.kim@samsung.com]
> > Sent: Monday, November 18, 2013 8:29 AM
> > To: Chao Yu
> > Cc: linux-fsdevel@vger.kernel.org; linux-kernel@vger.kernel.org; linux-f2fs-devel@lists.sourceforge.net; 谭姝
> > Subject: Re: [f2fs-dev] [PATCH V2 1/2] f2fs: add a new function to support for merging contiguous read
> > 
> > Hi Chao,
> > 
> > 2013-11-16 (토), 14:14 +0800, Chao Yu:
> > > For better read performance, we add a new function to support for merging contiguous read as the one for write.
> > 
> > Please consider 80 columns for the description.
> > I cannot fix this at every time though. :(
> 
> Got it, sorry about my carelessness in previous patch.
> 
> > 
> > >
> > > v1-->v2:
> > >  o add declarations here as Gu Zheng suggested.
> > >
> > > Signed-off-by: Chao Yu <chao2.yu@samsung.com>
> > > Acked-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
> > > ---
> > >  fs/f2fs/data.c |   45 +++++++++++++++++++++++++++++++++++++++++++++
> > >  fs/f2fs/f2fs.h |    4 ++++
> > >  2 files changed, 49 insertions(+)
> > >
> > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > > index aa3438c..18107cb 100644
> > > --- a/fs/f2fs/data.c
> > > +++ b/fs/f2fs/data.c
> > > @@ -404,6 +404,51 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
> > >  	return 0;
> > >  }
> > >
> > > +void f2fs_submit_read_bio(struct f2fs_sb_info *sbi, int rw)
> > > +{
> > > +	down_read(&sbi->bio_sem);
> > 
> > Is there any reason to use down_read()?
> 
> Isn't that we use bio_sem to let w/r or w/w submitting be mutex?

As I examined the bio_sem, I think we don't need to use a semaphore for
read and write IOs.
Just it is enough to use a mutex for writes only.

> 
> > It seems that we need to declare sbi->bio_read and sbi->bio_write
> > instead of sbi->bio_sem.
> > In addition to that, we need to use down_write(&sbi->bio_read) here.
> 
> If so, it looks similar between (struct rw_semaphore) sbi->bio_read 
> and (struct bio *) sbi->read_bio.
> How about using read_bio_sem/rbio_sem to differentiate 
> from sbi->read_bio?

I think sbi->write_mutex and sbi->read_mutex are much better.

Could you refer the following patches?
Thanks,

-- 
Jaegeuk Kim
Samsung